Conductive polymer has been studied in recent years for its novel electrical and optical properties [R. B. Kaner and A. G. MacDiarmid, Scientific America, 258, 106 (1988)]. Because of its electrical conductivity, it can be used as conductive paints, as electrical connection in flexible electrical circuit boards, as electromagnetic shielding, and as anti-electrostatic coatings. Its optical property leads to potential application as light filters, as thin film light polarizer, as color variable paints, and as nonlinear optical materials. In addition, conducting polymer is an electroactive material that can be reversibly doped and undoped by electrochemical oxidation and reduction. This property leads to possible applications as rechargeable batteries, electrochromic display devices and electrochromic windows.
Common methods for synthesis of conducting polymers lead to intractable materials that are usually not amenable to industrial processing. For example, polyaniline in its conductive form is insoluble in solvents, so it is difficult to be solution-processed. Upon heating, polyaniline decomposes before melting, so it can not be melt-processed. Other conducting polymers also have similar problems of the lack of processability, and this has limited the practical application of conductive polymers.
Most conductive polymers are insoluble in its doped conductive form. Some conductive polymers can be made slightly soluble by converting into its de-doped insulator form. For example, undoped polyaniline has low solbility in N-methylpyrrolidinone and 80% acetic acid [Angelopoulos et al, Mol. Cryst. Liq. Cryst., vol. 160, p. 151-163 (1988).]. Articles formed from this solution is not electrically conductive and lacks certain desirable optical properties associated with conductive polymers. Re-doping of the solid is difficult and is likely to cause cracking of films due to the insertion of dopant molecules into dense solid.
A method has been devised to make solutions of polyaniline in its conductive form. Elsenbaumer [U.S. Pat. Nos. 4,983,322 and 5,006,278] used a certain organic polar solvent coupled with specific oxidative dopant to dissolve the undoped base form of polyaniline (emeraldine base). The procedure comprises synthesizing conductive polymer in aqueous acidic medium, treated with base, dried, and then redissolve with nitromethane solution of ferric chloride. The multi-step procedure is somewhat cumbersome and the dissolving process is slow. An additional disadvantage is that articles made from this prior procedure may be dedoped because the low molecular weight dopants are relatively easy to escape from the host polymer due to heat (evaporation) or due to dissolving into organic solvent or water.
In order to bind the dopants more strongly to keep the conductive polymer in the conductive form and at the same time provide solubility, there have been efforts to functionalize polyaniline with sulfonic group containing substituents. For example, a sulfonated polyaniline such as poly(aniline sulfonic acid) is soluble in strong acidic and basic aqueous solutions because the sulfonate group is solvated by water molecules [J. Yue, S. H. Wang, K. R. Cromack, A. J. Epstein, and A. G. MacDiarmid, J.Am.Chem.Soc., 113, 2665 (1991)]. Alternatively, long alkyl chain, or alkyl sulfonic chain can be covalently bonded to the aromatic rings of polyaniline to render solubility in either organic solvents or aqueous solvents [L. H. Dao, M. Leclerc, J. Guay and J. W. Chevalier, Synth. Metals, 29, E377 (1989)]. Unfortunately, the covalently bonded side chains invariably affect the electrical and optical properties of polyaniline because of disturbances on the electronic structure arising from the strong electronic effect of the sulfonic group or due to the steric hindrance imposed by a bulky substituent which twists the relatively planar structure of the un-substituted polyaniline and decreases the pi electronic conjugation.
An alternative method involves the formation of colloidal particles of conductive polymers (polypyrrole and polyaniline). In this method a steric stabilizer is chemically grafted onto the backbone of polypyrrole or polyaniline [S. P. Armes and B. Vincent, J. Chem. Soc., Chem. Commun. p. 288, (1987); S. P. Armes, J. F. Miller and B. Vincent, J. Coll. Interface Sci., 118, 410 (1987); J. Chem. Soc., Chem. Commun. 88 (1989); Armes et al, U.S. Pat. No. 4,959,180 and 4,959,126.] Since the steric stabilizer uses protonated vinylpyridine units to help stabilizing the colloid in the suspension, the colloid floculates in base solution. The colloidal particles are suitable for casting thin films but may not have sufficient fibrous morphology to allow for stretch or melt processing.
In a previous study of electrochromic device [Yang et al, U.S. patent application Ser. No. 373,195] an electrochemical synthesis method was used to make electrochromic polyaniline with desirable color-switching responses. The electrochromic material was made by electrolysis of a solution of polyelectrolyte and monomeric aniline [Hwang et al, Synthetic Metals, 29, E271-E276 (1989); Zhang et al, Synthetic Metals, 29, E251-E256 (1989), Zhang et al, MRS Symposium Proceedings, (1990); Hyodo et al, Electrochemical Acta, 36, 87-91 (1991)]. Such material is a solid containing the conducting polymer and the polyelectrolyte. The material made by electrochemical polymerization is insoluble in water and other organic solvents, therefore it is difficult to be used in solution processing. The electrochemical polymerization is not easy to develop the large scale production.
It is an object of this invention to provide a processable, electrically conductive polymer composition containing a molecular complex made by template-guided chemical polymerization.
It is a further object of this invention is to provide a template-guided chemical polymerization process for preparing molecular complex.
The present invention uses chemical polymerization to form molecular complex of polyelectrolyte and conducting polymer which is versatile for processing. The synthetic method is suitable for mass production and can be controlled to provide the desirable different properties of the molecular complex. We disclose here the synthetic method and the new materials of different processability:
(1) Aqueous and non-aqueous solutions of the conductive polymer complex that are useful for spraying or casting thin films of conductive polymer. PA1 (2) Colloidal suspension of the conductive polymer complex that are advantageous for coating, painting, printing or for compounding. PA1 (3) Solid state of the conducting polymer complexes that are advantageous for stretch, melt processing, or for compounding. PA1 (1) Aqueous and non-aqueous solutions of the conductive polymer complexes that are useful for spraying or casting thin films of conductive polymer. PA1 (2) Colloidal suspension of the conductive polymer complexes that are advantageous for coating, painting, printing or for compounding. PA1 (3) Solid state of the conducting polymer complexes that are advantageous for stretch, melt processing, or for compounding.